Paris introduced special heat wave measures. They included opening air-conditioned rooms to the public and phoning people who might be especially vulnerable to the heat, primarily the elderly and those who can't leave their homes for medical reasons.

Authorities warned that temperatures could surpass those of 2003, when thousands of people died — many of them retirees who had been left alone while younger relatives vacationed. The government at the time was criticized for failing to respond quickly or decisively enough and has since been extremely quick to react when temperatures start to rise.

Lila Djedide, 27, and her 60-year-old mother Mina, kept cool in Paris by eating ice cream. The heat is tough, Mina said, but it's better than the usual Paris rain.

After France, the United Kingdom will feel the northern edge of the hot air mass on Wednesday when temperatures could hit 35 C (95 F), with the warm front possibly blowing Saharan sand into Britain. Both France and the U.K. issued heat alerts.

Temperatures in England started climbing higher Tuesday, with a maximum of just over 30 C (86 F) recorded at Heathrow airport in London, British meteorologists said. On the second day of the Wimbledon tennis tournament, some spectators fanned themselves and used umbrellas for shade from the scorching sun.

British trains were ordered to run slower than usual for fear rails would buckle in the heat, while health officials advised children and people with lung conditions to take precautions to stay cool and drink plenty of water.

Nicola Maxey of Britain's Met Office said the heat would begin to taper off from Thursday.

Italian authorities forecast temperatures of up to 36 C (97 F) — several degrees above average for this time of year — and also warned of the potential harmful effects on public health.

To get away from the approaching heat, Emeritus Pope Benedict XVI left the Vatican and headed to the cooler papal summer residence at Castel Gandolfo.

Spain and Portugal issued weather alerts Monday, advising residents to take extra care, as the heat plume passed through the Iberian Peninsula. Temperatures hit 44 C (111 F) in the southern Jaen province Tuesday, though it was cooler in Portugal.

As thermometers reached 37 C (99 F) in Madrid, 37-year-old store assistant Maria Cerezo said the heat was "oppressive" and made it hard to sleep at night.

"I never thought I'd say this, but I'm better off at work where there is air conditioning," she said.

Jesus Gutierrez, a 51-year-old who runs a small kiosk selling cold drinks and ice creams by the Spanish capital's popular Plaza de Colon square, said he has been selling so many bottles of water that he doesn't have time to chill them properly in the fridge before selling them.

"Water, water, water, that's all people ask me for," he said.

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Lori Hinnant and Maggy Donaldson in Paris, Jill Lawless in London and Jorge Sainz in Madrid contributed to this report.